Rosetta is the first mission designed to orbit and land on a comet. It consists of an orbiter, carrying 11 science experiments, and a lander, called 'Philae', carrying 10 additional instruments, for the most detailed study of a comet ever attempted.

Rosetta gets its name from the famous Rosetta stone that led to the deciphering of Egyptian hieroglyphics almost 200 years ago. Similarly, scientists hope that Rosetta will unlock the mysteries of how our solar system evolved.

Rosetta's launch was originally scheduled for January 2003 on an Ariane-5 rocket. Rosetta's target at that time was comet 46P/Wirtanen, with the encounter planned for 2011. However, following the failure of the first Ariane ECA rocket, in December 2002, ESA and Arianespace decided not to launch Rosetta during its January 2003 launch window. This meant that Rosetta's intended mission to comet 46P/Wirtanen had to be abandoned.

In May 2003, a new target comet was selected: the spacecraft was launched in March 2004. Rosetta met up with its new target comet 67P/Churyumov-Gerasimenko, on 6 Aug. 2014.

Objectives

ESA's comet-chaser will be the first to undertake a lengthy exploration of a comet at close quarters. After entering orbit around comet 67P/Churyumov-Gerasimenko in August 2014, Rosetta will release its Philae small lander onto the icy nucleus (November 2014).

Rosetta will orbit the comet for about a year as they head towards the sun. Once they have passed perihelion (closest distance to the sun), Rosetta will keep orbiting the comet for another half year.

As the most primitive objects in the solar system, comets carry essential information about our origins. Their chemical compositions have not changed much since their formation, therefore reflecting that of the solar system when it was very young and still unfinished, more than 4,600 million years ago. By orbiting comet 67P/Churyumov-Gerasimenko and landing on it, Rosetta will allow us to reconstruct the history of our own neighborhood in space.

Rosetta will also help to discover whether comets contributed to the beginnings of life on Earth. Comets are carriers of complex organic molecules, delivered to Earth through impacts, and perhaps played a role in the origin of life. Moreover, volatile light elements carried by comets may also have played an important role in forming Earth's oceans and atmosphere.

During its trek to comet 67P/Churyumov-Gerasimenko, Rosetta made two excursions to the main asteroid belt that lies between the orbits of Jupiter and Mars. Scientists identified two target asteroids along Rosetta's path, (2867) Steins and (21) Lutetia, which the spacecraft visited in 2008 and 2010.